A U.S. official, who was briefed on the investigation but is not authorized to speak publicly and spoke on the condition of anonymity, said Monday that investigators believe Martinez may have fallen into a culvert near Van Horn.

The official says Martinez's partner also suffered traumatic head injuries and can't remember what happened.

On Monday, an official said the incident occurred after dark in an area that's known for drug activity and where agents often look for drugs in culverts.`

Jose Martinez told the El Paso Times on Monday that doctors said his son suffered serious injuries that left his head "destroyed," and experience repeated ed cardiac arrest before he died.

Jose Martinez says he told his son that his job was too dangerous, but Rogelio Martinez enjoyed his work and wanted to defend the U.S. from terrorists and drugs traffickers.